The vast majority of micro-electronic devices are formed in silicon. Over the last several decades, a substantial effort has been directed to refining the reliability and manufacturability of these devices. As a result, silicon-based microelectronic devices have become dependable and inexpensive commodity items. Particularly, Complementary Metal Oxide Semiconductor (CMOS) technology has become a multi-billion industry providing the basis manufacturing technology for nearly 90% of all electronic commodities to society. Furthermore, Silicon-on-Insulator (SOI) technology is regarded as a future basis technology for combining optoelectronics technology with mainstream electronics manufacturing technology.
It is to be assumed that the current state of the art focuses on 1100 nm and above 1100 nm optical communication systems for application in CMOS and SOI, mainly as a result of compatibility with long haul optical fibre communication networks. This approach has severe limitations since it requires the incorporation of Ge in the systems in order to realize efficient detectors, and or III-V technology using hybrid approaches in both material and processing procedures. These technologies are extremely complex and also very expensive.
To take advantage of the existing silicon-based knowledge and infrastructure, there is a great interest in integrating active optical components into CMOS and SOI silicon technologies.
Silicon, however, is an indirect band gap semiconductor material which, unlike a direct band gap semiconductor material, has low photon emission efficiency. As a result, silicon is considered a poor source of electroluminescent radiation.
Although the photon-generation mechanism is not well understood, one source of visible light from silicon is a reverse biased p-n junction under avalanche breakdown conditions. Avalanche breakdown occurs when the p-n junction is reverse-biased to the point of where the electric field across the junction accelerates electrons such that they have ionizing collisions with the lattice. The ionizing collisions generate additional electrons which, along with the original electrons, are accelerated into having additional ionizing collisions. As this process continues, the number of electrons increases dramatically in a very short period of time, producing a current multiplication effect. A small percentage of these collisions results in photonic emissions through intra-band carrier relaxation effects, and inter-band carrier recombination effects.
Building on this principle, Snyman, et al. in an article “A Dependency of Quantum Efficiency of Silicon CMOS n pp LEDs on Current Density, IEEE Photonics Technology Letters, Vol. 17, No. 10, October 2005, pp 2041-2043”, have reported that the efficiency of light emission from silicon in such avalanching Silicon Light Emitting Device (Av Si LED) can be substantially increased by utilizing a reverse biased p-n junction with a wedge-shaped tip that confines the vertical and lateral electric field.
Several versions of optical waveguides have recently been realized using CMOS and SOI technology. These comprise either using an internal reflection mechanism or a rib wave-guided mechanism where optical modes are propagated laterally along the rib length. Some first iteration optoelectronic integrated circuits have been realized in CMOS technology utilizing CMOS processing technology, comprising of Si CMOS LED element, internal refection based waveguide using field oxide and SI N and dedicated detector elements using specially designed lateral incident detectors, all designed and processed in CMOS technology and designed by Snyman et al. Lately, Rowe et al. have realized more advanced and more efficient wave-guides in CMOS have been reported on using a rib design and mainly utilizing field oxide processing techniques in L. K. Rowe, M. Elsey, E, Post, N. Tarr, A. P. Knights, “A CMOS compatible rib waveguide with local oxidation of silicon isolation”, Proc. SPIE 6477, 64770L, (2007). Some more advance simulation of waveguide propagation in CMOS over-layers has recently been reported upon as disclosed in the article by L. Snyman et al., “Application of Si LED's (450 nm-750 nm) in CMOS Integrated Circuitry based MOEMS—Simulation and Analysis”, Proc. SPIE 7208, 72080C, (2009).
The utilization of Si nitride based over-layers as well Si Oxi Nitride based over-layers and coupling of light from Si LEDs as embedded in the Silicon substrates and CMOS wells into and out of these over-layers by means of special optoelectronic modules seems especially most viable, since it has recently been established that these materials are essentially transparent with low loss in dB per cm for above 650 nm radiation.
Accordingly, there is a need in the art to provide further improvements to both silicon based LED devices and wave guide technologies in the regime 650-850 nm.